Semiconductor light emitting devices include materials that emit light. For example, light emitting diodes (LEDs) are devices that use diodes, to which semiconductors are bonded, convert energy generated by the recombination of electrons and holes into light, and emit the light. The semiconductor light emitting devices are widely used in applications such as lighting, display devices and light sources, and the development thereof has been expedited.
In general, semiconductor junction light emitting devices have a junction structure of p-type and n-type semiconductors. In the semiconductor junction structure, light may be emitted by the recombination of electrons and holes at junction regions of both types of semiconductors, and further an active layer may be formed between both types of semiconductors in order to activate light emission. The semiconductor junction light emitting devices have a vertical structure and a horizontal structure according to the positions of electrodes for semiconductor layers. The horizontal structure includes an epi-up structure and a flip-chip structure.
FIG. 1 is a view illustrating a horizontal semiconductor light emitting device according to the related art and FIG. 2 is a cross-sectional view illustrating a vertical semiconductor light emitting device according to the related art. For convenience of explanation, in FIGS. 1 and 2, a description will be made on the assumption that an n-type semiconductor layer is in contact with a substrate and a p-type semiconductor layer is formed on an active layer.
First, a horizontal semiconductor light emitting device will be described with reference to FIG. 1.
A horizontal semiconductor light emitting device 1 includes a non-conductive substrate 13, an n-type semiconductor layer 12, an active layer 11, and a p-type semiconductor layer 10. An n-type electrode 15 and a p-type electrode 14 are formed on the n-type semiconductor layer 12 and the p-type semiconductor layer 10, respectively, and are electrically connected to an external current source (not shown) in order to apply voltage to the semiconductor light emitting device 1.
When voltage is applied to the semiconductor light emitting device 1 through the electrodes 14 and 15, electrons move from the n-type semiconductor layer 12 and holes move from the p-type semiconductor layer 10, which results in the recombination of the electrons and the holes to emit light. The semiconductor light emitting device 1 includes the active layer 11 and the light is emitted from the active layer 11. In the active layer 11, the light emission of the semiconductor light emitting device 1 is activated and light is emitted. In order to make an electrical connection, the n-type electrode 15 and the p-type electrode 14 are positioned on the n-type semiconductor layer 12 and the p-type semiconductor layer 10, respectively, with the lowest contact resistance values.
The positions of the electrodes may be varied according to substrate types. For instance, in the case that the substrate 13 is a sapphire substrate that is a non-conductive substrate as shown in FIG. 1, the electrode of the n-type semiconductor layer 12 cannot be formed on the non-conductive substrate 13, but should be formed on the n-type semiconductor layer 12.
Therefore, when the n-type electrode 15 is formed on the n-type semiconductor layer 12, parts of the p-type semiconductor layer 10 and the active layer 11 that are formed at an upper side are consumed to form an ohmic contact portion. Since the electrodes are formed in this way, a light emitting area of the semiconductor light emitting device 1 is reduced, and thus luminous efficiency also decreases.
In order to solve a variety of problems including the above-described problems, a semiconductor light emitting device that uses a conductive substrate, rather than the non-conductive substrate, has appeared.
A semiconductor light emitting device 2, as shown in FIG. 2, is a vertical semiconductor light emitting device. Since a conductive substrate 23 is used, an n-type electrode 25 may be formed on the substrate. Although, as shown in FIG. 2, the n-type electrode is formed on the conductive substrate 23, a vertical light emitting device may also be manufactured by growing semiconductor layers by using a non-conductive substrate, removing the substrate, and then directly forming an n-type electrode on an n-type semiconductor layer.
When the conductive substrate 23 is used, since voltage can be applied to an n-type semiconductor layer 22 through the conductive substrate 23, an electrode may be formed directly on the substrate.
Therefore, as shown in FIG. 2, the n-type electrode 25 is formed on the conductive substrate 23 and a p-type electrode 24 is formed on a p-type semiconductor layer 20, thereby manufacturing a semiconductor light emitting device having a vertical structure.
However, in this case, particularly in the case that a high-power light emitting device having a large area is manufactured, an area ratio of the electrode to the substrate needs to be high for current spreading. As a result, light extraction is limited and light loss is caused due to optical absorption, and further luminous efficiency is reduced.
The horizontal and vertical semiconductor light emitting devices, which are described with reference to FIGS. 1 and 2, have a reduced light emitting area to reduce luminous efficiency, limit light extraction, and cause light loss due to the optical absorption.
For this reason, a semiconductor light emitting device having a new structure needs to be urgently developed in order to solve the problems of the conventional semiconductor light emitting devices.